Quasi-diabatic States from Active Space Decomposition.

Area of Science:

• Quantum chemistry
• Computational physics
• Theoretical chemistry

Background:

• Accurate modeling of excited-state dynamics is crucial for understanding photochemical and photophysical processes.
• Existing methods often face challenges in computational cost and scalability for complex molecular systems.
• The quasi-diabatic representation offers a framework to simplify the description of electronic dynamics.

Purpose of the Study:

• To present a novel ab initio theoretical framework and efficient algorithms for computing model Hamiltonians of excited-state dynamics.
• To enable accurate simulations of energy transfer processes in molecular systems.
• To demonstrate the versatility and efficiency of the developed computational approach.

Main Methods:

• Utilizing a multiconfiguration electronic structure method known as the active space decomposition method (ASD).
• Constructing quasi-diabatic basis states from physical fragment states within the ASD framework.
• Implementing an efficient tree-based algorithm for computing and reusing intermediate tensors.

Main Results:

• Demonstrated the efficiency and parallel scalability of the developed algorithms through reported wall times.
• Successfully applied the method to model electron, hole, and triplet energy transfers in molecular dimers.
• Validated the computational approach for its accuracy and performance.

Conclusions:

• The presented ab initio theory and algorithms provide an efficient and versatile tool for studying excited-state dynamics.
• The active space decomposition method (ASD) combined with efficient tensor computation facilitates accurate modeling of energy transfer.
• This work advances the capability for simulating complex quantum dynamics in molecular systems.